Tobacco addiction imposes a significant negative impact on the health and economic status of the individual and society. The main psychoactive component in tobacco responsible for addiction is nicotine, which may also be consumed in alternate forms (e.g., vaporized liquid in e-cigarettes) with similar abuse potential. Unfortunatel, the vast majority of currently available pharmacotherapeutics for nicotine dependence are marginally effective in promoting long-term abstinence. Thus, a pressing need exists to identify novel targets for therapeutic development through innovative approaches/perspectives. Interestingly, the cerebrospinal fluid (CSF)-neuronal interface is beginning to emerge as a critical regulator of neural function and pathology. The choroid plexus and CSF provide a rich source of signaling molecules, and recent reports have uncovered the presence of a multitude of functional microRNAs (miRNAs). Past investigations into epigenetic regulation of gene expression have focused on signaling within the neurons themselves. However, we contend that this focus needs to be expanded to recognize the importance of intercellular communication via the extracellular environment. In this proposal, we will investigate circulating miRNAs from the CSF and establish their role in mediating gene expression in the habenula. Further, we predict that this will result in altered behavioral responses and consumption of nicotine. By identifying these novel extracellular mechanisms mediating nicotine reinforcement and reward, we hope to ascertain important insights into the persistence of the tobacco habit in human smokers/nicotine users. Moreover, identified circulating miRNAs have the potential to serve as biomarkers for nicotine addiction. It should also be noted that the choroid plexus is considered a main entry point for viral access into the brain via the CSF, and as such, an increased understanding of these processes may have broad implications for the pathogenesis of other human conditions, such as HIV/AIDS. In conclusion, findings from these investigations have to potential to significantly advance the field of epigenetic regulation of substance abuse, and in doing so, may induce a paradigm shift from an intracellular focus on neuronal function in addictive processes to recognize the importance of extracellular mechanisms. Through these efforts, we may achieve our overarching goal of identifying novel targets for the development of more efficacious therapeutics to treat nicotine dependence.